1. Field of the Invention
This invention relates principally to designer's triangles, and more particularly to triangles wherein a single implement has the capabilities of most of the known triangles, and thus eliminates the need for the use of at least two different triangles to perform designated tasks.
2. Description of the Prior Art
There are numerous triangles and protractors known in the art, and many are commercially available. One common form includes means for setting an adjustable angle which can be used to produce many different angles, as well as read angles off of drawings. Such equipment, however, is obviously subject to shifting and moving, if not exactly positioned or tightened, and thus requires a great deal of care in order to prevent errors in making drawings. In addition, in classroom drafting situations, protractors that have a plurality of holes, variable curvature arcs, a scale, and a few defined angles are well known. However, this type of unit does not provide for the production of numerous angles, and requires other equipment to produce drawings with angles other than the normal 30.degree. and 45.degree. angles provided on these units.
U.S. Pat. No. 2,080,620 discloses a drafting implement providing 15.degree., 30.degree., 45.degree., 60.degree., and 90.degree. angles but, due to its four-sided "boomerang" shape, it only allows for a 15.degree. angle from the horizontal. Additionally, due to its shape, a straight edge is not provided along two of the sides for use directly adjacent a tee square. Thus this instrument lacks the versatility of a triangular instrument, and other devices would be needed for efficient designing and drafting.
Swiss Pat. No. 276,736 of Clerc discloses a number of shapes formed of sheet plastic, including triangular shapes. Some of these shapes are provided with internal cutouts to provide additional straight edges at selected angles with the outside edges of the shape. One particular shape is a 45.degree., 60.degree., 75.degree. triangle with an internal triangular cutout having its edges oriented at 15.degree. to corresponding adjacent external edges.
Australian Pat. No. 127,143 of Calvert discloses a number of right triangular shapes formed of sheet plastic having an internal triangular cutout with one internal edge parallel to a corresponding adjacent external edge and the other two internal edges being at 15.degree. to their respective corresponding adjacent external edges.
French Pat. No. 1,022,765 of Queret discloses a quadrilateral shape of sheet plastic or the like in the form of two right triangles placed edge to edge along their hypotenuses. The quadrilateral shape has a plurality of internal cutouts resembling various geometrical shapes.
Other examples of drafting implements, straight edges and linear measurement instruments may be found in British Pat. No. 667,634 of Bradler, French Pat. Nos. 908,490 of Picard and 1,086,675 of Eggimann, Swiss Pat. No. 154,211 of Wolf, Italian Pat. No. 301,443 of Del Moro and German Pat. Nos. 585,040 of Ruckert et al and 865,714 of Beckenlechner.